The present disclosure relates to subject matter contained in Japanese Patent Application No. Hei-11-214666 filed on Jul. 29, 1999, which is expressly incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a camera having a motor-driven zoom lens and a motor-driven film-advance mechanism.
2. Description of the Related Art
There have been known various cameras having both a motor-driven zoom lens and a motor-driven film-advance mechanism. Some of them use two separate electric motors for driving the zoom lens and the film-advance mechanism, respectively. Others use a single electric motor for providing a drive torque, and a drive train for selectively transmitting the drive torque of the motor either to the zoom lens or to the film-advance mechanism in accordance with operations of a shutter release button and a zoom control knob, each provided on the body of the camera for user""s operation.
Conventional cameras using two separate electric motors tend to be relatively heavy and massive because an electric motor itself is an inherently heavy and massive component. Cameras using a single electric motor may have a somewhat reduced weight due to elimination of a second electric motor. However, they require a drive train for selectively transmitting the torque of the motor either to the zoom lens or to the film-advance mechanism. Conventional drive trains used for this purpose are relatively complicated in arrangement, occupy a relatively large space in the camera, may often have insufficient durability and require cumbersome assemblage process. Also, a typical, conventional drive train may include a pair of electromagnetic clutches controlled by electrical control signals, which clutches are relatively heavy and costly.
In view of the foregoing, it is an object of the present invention to provide a camera having a motor-driven zoom lens and a motor-driven film-advance mechanism, in which a single electric motor is used to selectively drive the zoom lens and the film-advance mechanism through a unique drive train, which may be simple in construction, may occupy only a small space in the camera, may provide a good durability and may be lightweight.
In accordance with the present invention, there is provided a camera comprising: a camera body; a zoom lens capable of continuous zoom operation between a longest-focal-length end and a shortest-focal-length end; a film-advance mechanism for advancing a roll of film loaded in the camera; and a zoom control knob provided on the camera body for camera user""s operation. The zoom control knob has three positions including an inoperative position for inactivating zoom operation and first and second operative positions for activating zoom operation toward the longest-focal-length end and zoom operation toward the shortest-focal-length end, respectively.
The camera further comprises a drive power unit including an electric motor for providing a drive torque; a motor control for controlling energized/de-energized state and rotating direction of the motor; and a drive train. The drive train is cooperative with the zoom control knob and operatively interconnects the drive power unit, the zoom lens and the film-advance mechanism, for selectively allowing the zoom lens and the film-advance mechanism to be driven by the drive power unit in accordance with current position of the zoom control knob.
In an embodiment, the drive power unit has an output shaft for outputting a drive torque. The zoom lens has an input member to be driven to achieve zoom operation. The film-advance mechanism has an input member to be driven to achieve film-advance operation. Further, the drive train operatively interconnects the output shaft of the drive power unit, the input member of the zoom lens and the input member of the film-advance mechanism.
The drive train may comprise a planetary gearing system having a sun gear, a planetary carrier-and-gear-wheel assembly and a ring gear, which are supported for rotation about a common axis. The planetary carrier-and-gear-wheel assembly may include one or more planetary gear wheels in engagement with both the sun gear and the ring gear so as to transmit a drive torque among the sun gear, the planetary carrier-and-gear-wheel assembly and the ring gear. The sun gear, the planetary carrier-and-gear-wheel assembly and the ring gear may be operatively connected to the output shaft of the drive power unit, the input member of the zoom lens and the input member of the film-advance mechanism, respectively. The planetary gearing system may be constructed such that the ratio of a drive torque acting on the ring gear to that acting on the planetary carrier-and-gear-wheel assembly is greater than the ratio of a required torque for the ring gear to achieve film-advance operation to that for the planetary carrier-and-gear-wheel assembly to achieve zoom operation, so that energizing the motor will cause rotation of the ring gear and no rotation of the planetary carrier-and-gear-wheel assembly unless the former is prevented from rotation. Finally, the drive train may further comprise a ring-gear-rotation preventing mechanism, which is inactive when the zoom control knob is at the inoperative position while active when the zoom control knob is at one of the first and second operative positions to prevent rotation of the ring gear.
The ring-gear-rotation preventing mechanism may comprise a clamp mechanism for clamping the ring gear to prevent rotation thereof when the zoom control knob is at one of the first and second operative positions.
The clamp mechanism may comprise a coiled spring secured to the camera body and surrounding a portion of the ring gear. In such a case, the zoom control knob may be supported by the camera body for movement between the first and second operative positions, with the inoperative position being defined between the first and second operative positions, and the coiled spring may have two end arms each engageable with both the camera body and the zoom control knob such that the coiled spring is tightened against and thereby clamps the portion of the ring gear to prevent rotation of the ring gear when the zoom control knob is at one of the first and second operative positions while the coiled spring is loosened from and thereby releases the portion of the ring gear to permit rotation of the ring gear when the zoom control knob is at the inoperative position.
The film-advance mechanism may comprise a film take-up spool of a generally hollow cylindrical shape having an axis. In such a case, the drive power unit may be of a generally cylindrical shape having an axis, with which the output shaft of the drive power unit is coaxial. Also, the drive power unit may be disposed in the film take-up spool such that the axis of the drive power unit and the axis of the film take-up spool are both coaxial with the planetary gearing system.
The drive power unit may further include a reduction gear box associated with the electric motor.
The camera may further comprise first and second electrical switches to be actuated by the zoom control knob when the zoom control knob is actuated into the first and second operative positions, respectively, and the motor control may control the rotating direction of the electric motor in response to open/close conditions of the electrical switches.